1. Field of the Invention
The present invention relates to a polymer electrolyte fuel cell stack using a polymer having ion conductivity as an electrolyte.
2. Description of the Related Art
FIG. 6 is a vertical sectional view for explaining an example of prior art (Jpn. Pat. Appln. KOKAI Publication No. 1-140562) of a polymer electrolyte fuel cell stack disclosed in Japan.
In this polymer electrolyte fuel cell stack, a plurality of unit cell main components 7 are mechanically stacked in the vertical direction, and the unit cell main components 7 are electrically connected in series with each other.
Each unit cell main component 7 includes a membrane electrode assembly 3 and separator 5. The membrane electrode assembly 3 is obtained by forming a fuel electrode 2a and oxidizer electrode 2b on the opposing plate surfaces of a proton exchange membrane 1.
In the membrane electrode assembly 3, several through holes for forming a plurality of manifolds are formed in the left and right edges in the vertical direction of the proton exchange membrane 1. The separator 5 functions as a fuel side collector and oxidizer side collector, and has a fuel gas flow path 9a and oxidizer gas flow paths 9b. A seal 6 is formed between the peripheries of the proton exchange membrane 1 and separator 5 in the vicinities of electrodes 2a and 2b. 
Since the proton exchange membrane 1 also has a function of preventing mixing of reactant gases supplied to the electrodes 2a and 2b, the area of the proton exchange membrane 1 is normally larger than that of the electrodes.
In the upper and lower end portions of the stack in which the plurality of unit cell main components 7 are stacked, current extracting plates 31, insulating plates 32, fastening plates 33, fastening jigs (fastening studs 34 and springs 35), a fuel gas supply pipe 36, a fuel gas exhaust pipe 37, an oxidizer gas supply pipe 38, an oxidizer gas exhaust pipe 39, a water supply pipe 40, and a water discharge pipe 41 are arranged.
Current extracting cables are placed in the current extracting plates 31 and connected to an external load. Also, the fastening plates 33 are required to be rigid in order to fasten the whole stack evenly.
The stack is required to make various conditions, such as the reactant gas flow, water flow, temperature, and humidity in the stacking direction, as even as possible in all the stacked unit cells 7.
In conventional polymer electrolyte fuel cell stacks before the above prior art, cooling means for discharging heat generated by power generation is generally a system by which a cooling plate in which a coolant such as pure water or an anti-freeze flows is inserted between unit cell main components.
In the above prior art, however, by supplying water (pure water) to the fuel electrode 2a through the fuel gas supply flow path 9a, a cooling plate can be eliminated by evaporating water moved from the fuel electrode 2a to the oxidizer electrode 2b and water generated by the oxidizer electrode 2b, in addition to the humidifying function of the proton exchange membrane 1.
Unfortunately, the above-mentioned prior art of the polymer electrolyte fuel cell stack has the following problems.
(1) If water stays in the fuel gas flow paths, not only the flow of the water but also the flow of the fuel gas or oxidizer gas becomes nonuniform in some cases to produce a large unit cell voltage distribution in the stack, and make stable power generation impossible. Similarly, when the stack is activated or stopped, water sometimes readily stays in the fuel gas flow paths to pose the same problem.
(2) The flow of water to be supplied to the fuel gas becomes nonuniform in some cases depending on the stack installation conditions, e.g., if the installation angle changes or vibrations occur. This sometimes produces a distribution of the humidifying conditions or latent heat cooling amount of each unit cell, thereby making stable power generation impossible.
An aspect of the present invention provides a polymer electrolyte fuel cell stack in which no water stays in gas flow paths, and which can stably generate electric power regardless of, e.g., the stack installation angle or vibrations.